Tire stud

ABSTRACT

A tire stud having a body with a hard wear resistant pin mounted an axial bore in the body thereof and protruding from one end of the body. The body has a head on the other end and is mounted in the tread of a tire head end foremost with the end of the stud from which the pin protrudes about at the level of the surface of the tire tread or projecting slightly therefrom. The stud according to the present invention is particularly characterized in that the pin moves axially into the stud body as the stud wears thereby controlling the amount of the pin of the stud which protrudes from the end of the stud body.

mte i States Patent 1 1 3,757,841 Cantz [451 Sept. 11, 1973 TIRE STUDPrimary Examiner-James B. Marbert [75] Inventor: Rolf J. Cantz, GroveCity, Pa. Att0mey Me]vm Crosby [73] Assignee: Kennametal, Inc., Latrobe,Pa. 57 ABSTRACT [22] Filed; O t, 29, 1970 A tire stud having a body witha hard wear resistant pin Appl. No.: 85,097

{52] US. Cl. 152/210 [51] Int. Cl. 1360c 11/16 [58] Field of Search267/210 V [56] References Cited UNITED STATES PATENTS 3,230,997 1/1966Carlstedt.... 152/210 3,477,490 11/1969 Carlstedt 152/210 mounted anaxial bore in the body thereof and protruding from one end of the body.The body has a head on the other end and is mounted in the tread of atire head end foremost with the end of the stud from which the pinprotrudes about at the level of the surface of the tire tread orprojecting slightly therefrom. The stud according to the presentinvention is particularly characterized in that the pin moves axiallyinto the stud body as the stud wears thereby controlling the amount ofthe pin of the stud which protrudes from the end of the stud body.

8 Claims, 16 Drawing Figures PATENTED$EP1 1 I915 3.751. 841

' SHEET 2 [IF 2 FIG-IO m 3 o 8 I if a 3' I I g 2% 8 J 1 r 7| i 25 "4 c 0E FIG-l2 FIG-l3 m 2 h. [I 2 it E /04 E U g ff 7 /06 E g [I2 110 E Q:PROTR us/o/v LENGTH OF PIN IN 500v FIG-I4 PIN MOVEMENT FORCE TO MOVE PININTO BODY LL INVENTOR.

ROLF J. C ANTZ BY TIRE s'run The present invention relates to tire studsand is particularly concerned with tire studs in which the protru sionof the hard pin from the outer end of the tire stud body is controlledso as to remain substantially constant throughout the life of the tire.

Tire studs are well known and the most popular type currently usedcomprises a stud body in the form of a cylinder having a single head onone end and having a hard wear resistant pin mounted on the axis of thestud body and protruding a short distance therefrom at the end oppositethe head. The studs vary in size and the hard wear resistant pin isusually on the order of about half the length of the stud or a littlemore.

Studs of the nature referred to above are inserted, head end foremost,in blind holes provided therefor in tire treads so that the pin end ofthe stud projects a short distance outwardly from the surface of thetire tread whereby the end of the stud will engage the surface on whichthe tire rolls. Such studs are employed for increasing the traction oftires on slippery surfaces such as snow and ice and are highly effectivefor this purpose.

Certain problems present themselves in connection with use of tire studsin tire treads, however, that can, on occasion, become extremelytroublesome. The bodies of the studs are generally made of metal, eithersolid metal or sintered from a metal powder, or from a relatively strongplastic, preferably reinforced, as by glass fibers. The pins in thestuds, in order to be sufficiently wear resistant, are formed of acemented metal carbide such as a tungsten carbide or a titanium carbidecomposition or a mixture of various hard carbides.

Heretofore, the hard pins have been compounded to have about the samewear rate as the rubber-like material of the tire tread in which theywere mounted so as to maintain substantially the same protrusion of thepin end of the stud from the tire tread throughout the life of the tireand stud.

The compounding of thematerial of the pin to match the wear rate of the,tread material of the tire has always been difficult and it is alwayspossible for the stud to be installed in a tire having tread materialdifferent from that for which the stud was designed. This isparticularly the case because substantially all studs are installed inretail outlets at the point of purchase of the tire in which' they aremounted andby tire recappers and the like.

When the wear rate of a tire stud pin does not match the wear rate ofthe tread material of the tire, either the pin wears off too rapidly andthe protrusion of the stud is'lost and the stud becomes less effective,or the tiretread material wears more rapidly than the pin and theprotrusion of the studincreases thereby leading to disadvantageousconditions.

More specifically, the disadvantageous conditions referred to are that,with too great a protrusion of the stud from the tread, the stud will bedeflected as the tire rolls on a roadway thus tending to loosen the studin the tire tread and also causing slipping of the pin on the roadwaythereby developing heat in the stud and also causing road wear. 7

Furthermore, when a stud protrudes excessively from a tire tread, thetraction of the tire on a clean dry road surface is reduced overwhat itwould be if the studs had the correct amount of protrusion and remainedupengages than if the stud were upright in the tire and,

therefore, presented endwise to the surface.

With the foregoing in mind, a primary objective of the present inventionis a construction for a tire stud of the nature referred to in which theproper amount of protrusion of the pin from the outer end of the studbody is maintained throughout the life of the stud.

Another object of the present invention is the provision of a tire studof the nature referred to which reduces road wear caused by the stud.

A still further object is the provision of a tire stud of the naturereferred to which runs cooler in operation than heretofore known studs.

A still further object of the invention is the provision of a tire studof the nature referred to which runs more quietly in operation. i

It is also an object of the present invention to provide a tire stud ofthe nature referred to which permits a greater latitude in the selectionof the carbide used for the pin in the stud and which permits the use ofa smaller amount of carbide. 1

These and other objects and advantages of the present invention willbecome more apparent upon reference to the following detailedspecificationtaken in connection with the accompanying drawings inwhich:

FIGS. 1 I through 6 are vertical sectional views through different studarrangements according to the present invention;

FIG. 7 is a plan sectional view indicated by line VII- VII on FIG. 6;

FIG. 8 is a view like FIG. 7 showing a modified arrangement;

FIG. 9 is a vertical sectional view indicated by line IX-IX on FIG. 8;

FIG. 10 is a composite view showing a stud according to the presentinvention at various stages during thelife thereof; I

FIG. 11 is a graph showing how the road impact on the tire stud pinvaries with the protrusion of the pin fromthe tire tread; f

FIG. 12 is a schematic view showing that the stud is impactedsubstantially in the axial direction as the tire rolls on a roadway; I

FIG. 13 is a graph showing the characteristics of a modification of theinvention wherein the force re quired to press a pin axially into thebody varies if the pin migrates into the body;

FIG. 14 is a graph showing the range in which pin movement into the bodyoccurs at different road impacts;

FIG. 15 is a vertical sectional view showing the details and dimensionsof a typical stud according to the present invention; and

FIG. 16 is a fragmentary view showing a modified form which the studbody can take.

BRIEF SUMMARY OF THE INVENTION The present invention is concerned with atire stud arrangement in' which a hard wear resistant pin is mounted ina bodywhich is, in turn, mounted in a tire tread with the pin projectingfrom the tire tread surface. The particular feature disclosed in thepresent application is that of the pin moving axially into the stud bodyas the tire tread and stud body gradually wear down in use. The pin maywear down simultaneously with the tire tread and stud body but at areduced rate, or the pin may be made of sufficient hardness that thewear thereon is diminished substantially at zero.

DETAILED DESCRIPTION Referring to the drawings somewhat more in detail,in FIG. 1, the stud illustrated comprises a body having a centralthrough bore 12 with a hard wear resistant pin 14 mounted in a bore 12at one end. Body 10 at the end opposite the end in which the pin 14 ismounted comprises a single radial flange 16 forming the head of thestud.

The bore 12 at the head end thereof may be provided with a flaredportion 18 of selected diameter and degree of taper and which is ofimportance in that it provides space into which the material of a tiretread can be displaced when the stud is pressed radially inwardly in thetire tread as the tire in which the stud is mounted rolls on a roadway.

As is known, the studs are inserted head end foremost into blind holesprovided in the tire tread, the holes being substantially smaller indiameter than the stud body and the studs being inserted into the holeswith the stud heads resting on the bottoms of the holes and with atleast the outer end of the pin portion of the stud projecting outwardlyfrom the tread surface. In FIG. 1, the surface of a tire tread in whichthe stud is mounted is indicated by the line 20.

It is of importance for the outer end of pin 14 to maintain about thesame protrusion from the tread surface throughout the life of the tireand stud. The tread material of the tire has a certain wear rate and thematerial of the body of the stud is selected so that the wear ratethereof is at least as great as that of the tread material. Therelationship between the outer end of the stud body and the surface ofthe tread of the tire thus remains substantially consistant throughoutthe life of the tire and stud.

The pin l4, however, is formed of hard cemented carbide material such ascemented tungsten carbide or cemented titanium carbide, or a mixture ofcarbides, and is extremely hard. The pin can be compounded by selectingthe type of binder metal, usually cobalt, or nickel, or a mixturethereof, and the percentage of the binder metal that is admixed with thecarbides is selected to provide for a wear rate substantially matchingthat of the tire tread. The difficulty of matching the studs to the tiretread material in practice, however, prevents such selection of the wearrate of the carbide pin from being effective.

The studs are usually put into the tires at retail outlets, or byretreaders and the wear rates of the tire tread materials may varywidely and the matching of the stud pins with the tread material is thusvery difficult to accomplish in practice.

When the wearrate of the pins is not matched with the wear rate of thetread material, the pins either wear off too rapidly, thereby permittingthe studs to become ineffective, or the pins wear off too slowly therebyleading to excessive protrusion of the pins from the tire tread. Excessprotrusion leads to noisy operation of the studs, insufficient grippingpower of the studs on the road surface because tilting of the studs inthe tire tread, the generation of excessive heat in the studs due toslipping of the pins on the road surface as the studs deflect, andloosening of the studs in the tread material due to deflection of thestuds as they strike the roadway and due to deterioration of the treadmaterial because of the heat developed in the studs.

The stud according to the present invention avoids a condition ofexcessive protrusion of the pin from the tire tread, even where the wearrate of the pin is less than that of the tire tread, by permitting thepin to move axially into the stud body in a controlled manner as thetire tread and stud body wear away.

By this expedient, the necessity of close matching of the rate of wearof the stud pin to that of the tread material is eliminated and thestuds will remain more effective in use and road wear will be reducedwhile, furthermore, less material is required for the pins and thematerial of the pins can be almost entirely used up thereby representinga substantial economy.

In the modification of FIG. 1, the stud body 10 is formed of areinforced plastic material, for example, a

nection with tire studs and permit assembling of the pins in the studbodies without the use of cement or brazing because the studs can bepressed into the bore in the stud body small end foremost and will wedgetherein with an interference fit and will hold in the stud bodythroughout the life thereof.

Heretofore, however, it has not been contemplated that the pin will movein the stud body as the stud wears down and thus the tapering of the pinhas been provided merely for the purpose of facilitating assembly of thepin with the stud body and eliminating the cost and labor involved inconnection with a cementing'or brazing operation. A tire stud embodyinga tapered pin therein is illustrated and claimed in the U.S. CarlstedtPat. No. 3,230,997, assigned to the same assignee as the instantapplication.

In the modification of FIG. 1, wherein the body of the stud is formed ofa plastic material, the degree of taper on the pin is about 10includedangle between the opposite sides thereof. This degree of taperon a pin has not, heretofore, been used in respect of tire studs, to myknowledge, and represents that degree of taper which will permit thestud to wedge in the plastic body and which will support the pin in theplastic body but which will permit the pin to migrate axially inwardlyinto the stud body as the tire tread and stud body wear down in use.

It will be apparent that when the pin and stud are first assembled,there is a maximum length of pin engaged bythe stud body. For example,the pin 14, which may be about 0.104 to 0.107 inches in diameter at thelarger end, has about 0.040 to 0.060 inches thereof protrud-' ing fromthe outer end of the stud body and about 0.160 inches thereof locatedwithin the stud body. The total length of the pin is thus about 0.200inches which is substantially shorter than it has been possible to makepins heretofore, for the pins to remain effective throughout the life ofthe tire and stud.

In the arrangement of FIG. 1, as the stud body wears down with the treadmaterial, the amount of the pin which is gripped by the stud body isreduced and thus the force required to move the pin inwardly into thestud body is also reduced. In the case of the modification of FIG. 1, itis preferably for the pin to be so compounded as also to wear downsomewhat in use, but at a rate substantially less than the rate of wearof the stud body and the tire tread material.

The tire in rolling on a roadway will bring a stud properly mountedtherein into engagement with the roadway so that an impact is deliveredon the outer end of the pin of the stud. As long as the stud remainssubstantially radial in the tire, the impact on the stud as the tirerolls on the roadway is delivered in the axial direction thereof on theouter end of the stud pin.

The exact amount of this impact is not known, but is believed to be onthe order of 60 to 80 pounds and will, of course, vary with the speed ofrotation of the tire and other factors. I

Further, the entire stud will tend to move radially into the tire whenthe outer end of the stud impacts against the roadway and with theresistance to inward movement of the stud into the tire being at leastpartially under the control of the flared region 18 at the inner end ofthe central bore in the stud body.

As mentioned, the exact amount of the impact on the outer end of the pinis not known, but his sufficient to cause inward movement of the pininto the stud body when the stud body wears down at the outer end whilemaintaining the protrusion of the pin from the outer end of the studbody substantially constant.

In connection with stud bodies formed of reinforced plastic, thediameter of the bore 12 is substantially constant from end to end of thestud body with the exception of a short outwardly flared portion thatmay be provided at the pin end of the bore for assembly purposes. Such aflared lead-in portion in the bore permits the pin to be started easilyinto the bore and does not i in any way interfere with the movement ofthe pin into the body during operation of the stud according to thepresent invention.

In FIG. 2, the stud body 30 has a pin 32 mounted therein which is formedwith a taper of about 25 to 3, as shown. The body 30 in FIG. 2 is formedof sintered powdered metal, such as iron powder or the like and thecentral bore 34 in which the pin is mounted may be straight with aflared outer portion 36 at the head end of the stud.

As in connection with the stud of FIG. 1, pin 32 will migrate axiallyinwardly in bore 34 as the tire in which the stud is mounted rolls on aroadway and the stud body wears down thereby decreasing the grippingpower of the stud body on the pin 32.

Also, as in connection with the FIG. 1 modification, the pin 32 in FIG.2 may protrude about 0.040 to 0.060 inches from the stud body and mayhave about 0.160 inches thereof disposed in the stud body when the pinand body are newly assembled.

FIG. 3 shows a stud body 40 which is formed of solid metal, as on arivet making machine, and which body has a head 42 and a central bore 44in which a tapered pin 46 is mounted. The pin 46 in FIG. 3 has the sameamount of protrusion from the stud body as those of FIGS. 1 and 2 andthe same overall length but is formed with a taper of about 2.

The metal of the stud body is somewhat more firm than the plasticmaterial of the body of FIG. 1 or the sintered powdered metal body ofthe stud of FIG. 2 and a smaller angle of taper on the stud is requiredto permit the stud to migrate inwardly in the bore 44 of the stud body.As before, the bore 44 preferably has a flared region 48 in the head ofthe stud body.

FIG. 4 shows an arrangement wherein the stud body 50, and which may be asolid metal body made by a heading process, has a central bore 52 with aflared region 54 at the head end. The pin 56 is mounted in the bore ofthe stud body has an overall length the same as the pins previouslydescribed and has the same protrusion from the stud body.

In the case of the FIG. 4 modification, the bore 52 in the stud bodytapers inwardly toward 15' bottom at an included angle of about 15 toabout 30' and this arrangement will permit the previously describedgradual migration of the pin downwardly into the bore in the stud bodyas the body wears away while maintaining about the same protrusion ofthe pin from the body.

In FIG. 5, the stud body 60 has a straight bore 62 therethrough with aflared portion 64 at the head end of the stud and with a pin 66 mountedin the other end of the bore. Pin 66 has an included angle of about 3between the sides thereof and is of an extremely hard composition sothat it wears at an extremely slow rate.

In this case, the pin may have the same protrusion of about 0.040 to0.060 inches from the stud body but can have substantiallyless than0.160 inches thereof within the stud body because of the slow wear rateof the pin. It is not necessary for the pin to wear away for it to gripsnow and ice and in the case of FIG. 5, a short pin which wearsextremely slowly can be employed if the pin is permitted to migrateaxially inwardly into the stud body as the stud and tire wear away.

FIGS. 6 and 7 show a modification for obtaining corrtrolled inwardmigration of the pin into the stud body. In these figures, stud body 70has a head 72 at one end and a central bore 74 terminating in a flaredout portion 76 at the head end. A tapered hard wear-resistant pin 78 ismounted in the end of bore 74 opposite the head end and may taper at anincluded angle of about 3 from top to bottom.

The particular feature of the stud of FIGS. 6 and 7 is illustrated inFIG. 7 wherein it will be seen that bore 74 is provided with axialgrooves, or pockets, 80 circumferentially distributed therein anddecreasing in circumferential width toward the head end of bore 74. Withthisa'rrangement, the pin 78 is supported on land areas 82 between thepockets and these land areas gradually widen toward the head end of thestud.

By widening the land areas towardthe head end of the stud, as the studwears off in use so that the amount of the pin in the stud bore becomesshorter whereby less resistance would normally be offered to the pinbeing driven axially inwardly into the bore, the resistance to suchinward movement can be maintained about constant thereby permitting thepin of the stud to maintain substantially the original protrusion ofabout 0.040 inches from the outer end of the stud body.

FIGS. 8 and 9 show another vmodification in which the tapered pin ismounted in a bore 92 formed in the body 94 of the stud body. Bore 92 isprovided with circumferentially distributed flats 96 extendinglongitudinally in the bore and inclined so as to converge toward thehead end of the stud body. In this manner also the resistance to inwardmovement of the pin into the stud body remains about constant as the pinwears off and moves into the body and there is less length of the pingripped by the body.

Other arrangements for controlling the resistance of the pin to movementinwardly into the stud body will occur to those skilled in the art.

FIG. 10 more or less schematically illustrates the appearance of a studaccording to the present invention at various stages in the lifethereof. The view at the left side of FIG. 10 shows the stud newlyassembled and progressive stages in the wear thereof are shown towardthe right. For identification, the various stages are identified bycapital letters A through E with A representing the new stud and Erepresenting the stud when it is substantially completely worn away.

At stage E, when the stud and tire are about used up, the stud is movedinwardly a distance of about 0.235 inches.

It will be appreciated that the inward movement of the pin into the studbody permits the pin to be made substantially shorter than hasheretofore been possible and likewise permits the use of harder materialin the pin than has heretofore been possible.

Furthermore, the rate of wear of pin need no longer be matched to therate of wear of the tire tread but will automatically adjust in the studbody to have the proper amount of protrusion. The studs with inwardlymigrating pins according to the present invention do not protrudeexcessively from the tire tread and thus do not tilt in the tire andthereby slip excessively on the road surface, and thereby do not wearthe road surfaces as rapidly as conventional studs while,simultaneously, less heat is developed in the stud body thus preventingthe studs from becoming loose in the tire tread due to deterioration ofthe tread material.

Still further, the studs remain upright in the tire and are alwayspresented endwise to the road surface and thus operate efficientlythroughout the life of the tire and tread and are substantially morequiet in operation than studs with excessive protrusion from the tiretread.

Reference to FIGS. 1 1 to will serve further to clarify the nature ofthe present invention. FIG. 11 is a graph in which the protrusion of thepin of the stud .beyond the tire tread is plotted against the impactdelivered to the pin as the tire rolls on a roadway. Inasmuch as thestud body wears off so as to be substantiallyflush with the tread, itwill beunderstood that the protrusion of the pin from the surface of thetire tread is substantially equal to the protrusion of the pin from theouter end of the stud body.

In FIG. 11, the desired protrusion of the pin is indicated by the dottedline at 100 and the effective impact on the pin at the desiredprotrusion is indicated by the line 102.

As will be seen in FIG. 12, when the tire 104 rolls on a road surface106, a stud 108 in the tire which is approaching the road surface, willbe presented to the road surface substantially endwise as indicated byarrow 110 which is an arc struck from about the instantaneous center ofrotation of the wheel located at 11 2. From FIG. 12 it will beappreciated that the impacts referred to are deliverd substantiallyaxially of the pin in the stud body.

FIG. 13 is a graph showing the conditions that must be established in astud when both the pin and the body wear down in use. It is readilyperceivable that as the body wears down, there is less length of pin inthe body and, therefore, less force is required to drive the pin axiallyinto the body.

However, where both the pin and the body wear down, the length of pin inthe body necessarily decreases in order to maintain the same amount ofprotrusion of the pin from the body and this requires that theresistance offered by the body to axial movement of the pin per unitlength of the pin in the body increase. The ideal conditions are shownin FIG. 13 in which the length of pin in the body as is plotted againstthe resistive force offered by the body per unit length of pin thereinto movement of the pin in the body.

Thus, with the stud body configured and constructed to offer greater andgreater resistance per unit length of the pin therein to inward movementof the pin in the body, both the body and the pin can wear off in useand about the same amount of protrusion of the pin from the body will bemaintained throughout the life of the stud.

FIG. 14 graphically shows the conditions that obtain when the pin isformulated of a material that imparts such hardness to the pin that itwears very little during the life of the stud. Under thesecircumstances, about the same length of pin will always be located inthe stud body for the desired protrusion.

In this case, the bore of the body is so selected and configured thatsubstantially the same resistive force is developed thereby throughoutthe life of the stud against inward movement of the stud. The resistiveforce is, of course, the force per unit length of the pin in the studbody so that when the body wears off and the stud pin then has a greaterprotrusion and a shorter length in the body, the increased impacts onthe pin will drive it axially into the body and restore the originalconditions.

In FIG. 14, the desired protrusion of the pin from the stud body isindicated by the range between lines 114 and the force required to movethe pin axially into the body between those limits of protrusion forcelies between the lines 116. I

When the protrusion goes beyond the upper limit of the range 114, thepin will move axially into the body to bring the protrusion back towithin the range 114 and, should the pin protrusion be less than therange indicated by lines 114, no pin movement will occur till the bodywears down to the point that the proper amount of protrusion of the pinis restored.

FIG. 15 shows a typical stud according to the present invention with thepin merely dropped into the upper end of the bore in the stud body butnot yet pressed into position. In FIG. 15, the stud body is indicated at200 and the pin at 202. It will be observed that the pin is quite shortrelative to the limit of the body and this is possible according to thepresent invention because the stud migrates axially inwardly into thebore 204 in the stud body as the stud body wears down.

In the arrangement shown in FIG. 15, the diameter of the larger end ofthe pin, indicated at D1, might range from 0.104 to 0.107 while thediameter of the smaller end, indicated at D2, might range from 0.084 to0.087. The included angle between the sides of the stud is indicated as3, but can range down to 2.5.

The length of the stud body, indicated by dimension L, can be about0.400 to about 0.580 and the diameter of the head, indicated bydimension H may be about 0.300 to about 0.350.

The bore 204 in the stud body tapers inwardly toward the bottom at anincluded angle between the sides thereof of about 1 16'. At its extremeupper end, the diameter of the bore, indicated at D3, is about 0.100 andat the bottom, indicated at D4, is about 0.088. The diameter of theshank portion of the stud body, indicated at D5, ranges from about 0.198to 0.202.

The specific stud illustrated in FIG. 15 is merely exemplary of a numberof different forms which a stud body according to the present inventioncan take in order to provide for the inward movement of the pin into thestud body that has been described.

In FIG. 15, the bore in the stud body tapers uniformly inwardly from endto end but, with other materials, it might be desirable to taper the pinend of the bore at a greater angle than the remainder of the bore, oreven to make the remainder of the bore straight with no taper therein.

In FIG. 16, the bore 300 extending axially through the stud body 302 isprovided with an upwardly facing shoulder 304 near the body. Thisshoulder is provided to prevent the pin from being pushed completelythrough the stud body when the stud body is worn down and is near theend of its life because the pin pushing completely through the stud bodycould cause damage to the tire in which the stud is mounted.

Further, as has been described above, the bore may be configured otherthan circular in order to obtain the desired resistance to inwardmovement of the pin into the body and the change thereof per unit lengthof the pin in the body as has been described hereinbefore.

What is claimed is:

1. In a tire stud; a body comprising a cylindrical shank with a radialflange on the inner end thereof forming the head of the stud and anaxial bore extending into the shank from the outer end thereof, atapered pin of predetermined length formed of a material substantiallyharder and more wear resistant than the ma-- terial of said body andpress fitted small end foremost into said bore at said outer end of saidshank, said pin having a predetermined portion of the axial lengththereof in said bore and having an outer end protruding from said outerend of shank, said stud being adapted for insertion head end foremostinto a blind hole extending radially into a tire tread with the head ofthe stud engaging the bottom of the hole and the outer end of said pinprojecting radially from the surface of the tire tread, said pin havingan interference fit with said bore such that when the stud body andpin'are unworn the force required to move said pin axially inwardly insaid bore until said predetermined portion of the axial length of saidpin is disposed in said bore is equal to or only slightly greater thanthe force exerted on said pin as the tire in which the stud ismountedrolls on a road surface, whereby when the outer end of the shank of thestud wears down in use a predetermined amount at the pin end so as todecrease the axial length of the pin in said bore, the said pin willmove axially inwardly in said bore under the influence of the forceexerted thereon by the road surface so as to maintain the protrusion ofthe pin from said outer end of said stud body substantially constant,said body being formed of metal and including axially extendingcircumferentially spaced first regions engaging said pin and interveningsecond regions radially spaced from said pin.

2. A tire stud according to claim 1 in which said second regions narrowin a direction toward the head end of said bore.

3. A tire stud according to claim 2 in which said first regions defineportions of a right cylinder.

4. A tire according to claim 1 in which said bore includes a restrictedregion near the head of the stud substantially smaller in diameter thanthe smallest diameter of said pin to provide a stop for the pin so thatthe pin cannot emerge through the head end of the body.

5. A tire stud according to claim 1 in which said bore is square incross section and tapers inwardly toward the head end of said body at anincluded angle between opposite sides thereof on the order of about 1'to 2'.

6. A tire stud according to claim 1 in which said pin tapers at anincluded angle between the sides thereof on the order of about 2.

7. A tire stud according to claim 1 in which said body is sinteredpowdered metal.

8. A tire stud according to claim 1- in which said body is solid metal.

1. In a tire stud; a body comprising a cylindrical shank with a radialflange on the inner end thereof forming the head of the stud and anaxial bore extending into the shank from the outer end thereof, atapered pin of predetermined length formed of a material substantiallyharder and more wear resistant than the material of said body and pressfitted small end foremost into said bore at said outer end of saidshank, said pin having a predetermined portion of the axial lengththereof in said bore and having an outer end protruding from said outerend of shank, said stud being adapted for insertion head end foremostinto a blind hole extending radially into a tire tread with the head ofthe stud engaging the bottom of the hole and the outer end of said pinprojecting radially from the surface of the tire tread, said pin havingan interference fit with said bore such that when the stud body and pinare unworn the force required to move said pin axially inwardly in saidbore until said predetermined portion of the axial length of said pin isdisposed in said bore is equal to or only slightly greater than theforce exerted on said pin as the tire in which the stud is mounted rollson a road surface, whereby when the outer end of the shank of the studwears down in use a predetermined amount at the pin end so as todecrease the axial length of the pin in said bore, the said pin willmove axially inwardly in said bore under the influence of the forceexerted thereon by the road surface so as to maintain the protrusion ofthe pin from said outer end of said stud body substantially constant,said body being formed of metal and including axially extendingcircumferentially spaced first regions engaging said pin and interveningsecond regions radially spAced from said pin.
 2. A tire stud accordingto claim 1 in which said second regions narrow in a direction toward thehead end of said bore.
 3. A tire stud according to claim 2 in which saidfirst regions define portions of a right cylinder.
 4. A tire accordingto claim 1 in which said bore includes a restricted region near the headof the stud substantially smaller in diameter than the smallest diameterof said pin to provide a stop for the pin so that the pin cannot emergethrough the head end of the body.
 5. A tire stud according to claim 1 inwhich said bore is square in cross section and tapers inwardly towardthe head end of said body at an included angle between opposite sidesthereof on the order of about 1'' to 2''.
 6. A tire stud according toclaim 1 in which said pin tapers at an included angle between the sidesthereof on the order of about 2*.
 7. A tire stud according to claim 1 inwhich said body is sintered powdered metal.
 8. A tire stud according toclaim 1 in which said body is solid metal.